The asphalt industry produces multiple asphalt (bitumen) compositions in preparing aggregate compositions useful as road paving material, such as using bitumen pitch in combination with sand or gravel). The asphalt must meet defined parameters relating to properties such as viscosity, stiffness, penetration, toughness, tenacity and ductility for the specific application. For particular applications, conventional bitumen compositions can be modified by the addition of other substances, such as polymers. A wide variety of polymers have been used as additives in asphalts, to improve physical and mechanical performance properties. Polymer-modified asphalts are routinely used in the road construction/maintenance and roofing industries, and by incorporating into them an elastomeric-type polymer (e.g., a rubber, such as SBR or SBS rubber from Kraton Corp), which may be one such as butyl, polybutadiene, polyisoprene or polyisobutene rubber, ethylene/vinyl acetate copolymer, polyacrylate, polymethacrylate, polychloroprene, polynorbornene, ethylene/propylene/diene (EPDM) polymer and advantageously a random or block copolymer of styrene and a conjugated diene. The modified asphalts thus obtained commonly are referred to variously as bitumen/polymer binders or asphalt/polymer mixes or “modified asphalts.” It is also known that the stability of polymer-bitumen compositions can be increased by the addition of crosslinking agents, including vulcanizing agents such as sulfur, frequently in the form of elemental sulfur. The sulfur chemically couples with the polymer and the bitumen through sulfide and/or polysulfide bonds. See U.S. Pat. No. 6,133,351, and WO-2006-047044, and U.S. Pat. No. 6,569,351 all incorporated by reference. These sulfur crosslinked blends or formulations have demonstrated the ability to optimize the polymer addition, reduce production costs, increase production capacity, crosslink at less than 350° F., and improve the compatibility characteristics of the asphalt. The improved compatibility allows use of less expensive generic polymers such as Kraton D1101 (from Kraton Polymers, of Houston, Tex. (a Kraton Corp. company)) with a broad range of asphalts. As used herein, a crosslinking blend includes a sulfur product (not necessarily elemental sulfur) in a suitable carrier, such as, for instance a low viscosity petroleum based oil, for use in combination with modified asphalts.
One method to prepare a crosslinked composition for use in a modified asphalt product is to pre-mix an oil based blended product, containing other desired additives, such as crosslinking additives, accelerators, initiators, and H2S suppressants. The resulting premixed oil based product will later be added or mixed with the polymer asphalt product. For instance, one crosslinking material is AS-3000 Plus available from Alberty Additives, LLC in Baton Rouge, La., and contains a sulfur product in a petroleum oil, such as paraffinic petroleum oil with proprietary accelerators to facilitate rapid reaction of the rubber/polymer with the asphalt. These accelerators allow higher asphalt throughput in the production facility. The crosslinking material may include a proprietary dispersant. Another crosslinking product is BGA, U.S. Pat. No. 6,569,925 B2, from Ergon Armor (an Ergon, Inc. company) of Memphis Tenn., (hereby incorporated by reference).
In application, the crosslinking material is delivered in a container, such as in a 360-gallon barrel or a 275 gallon cone or frustrum tote container, to be mixed with the heated asphalt/polymer material. The crosslinking product is pumped from the tote, such as with a gear pump or air diaphragm pump, to be added to the asphalt polymer composition in specified dosages. Often, the crosslinking materials may be stored in the tote or barrel for a period of time, such as for two-three weeks, prior to being combined with the asphalt mixture. Solids in the tote-stored crosslinking product, over time, will settle out, requiring that the crosslinking product be mixed prior to adding to the asphalt/polymer (e.g., rubber) mixture.
Several techniques have been used to mix the crosslinking products, such as using a hand held blade shear mixer, or using a pulsed air system, such as a Pulsair portable wanded mixer (e.g., a 10-55 tote stick), from Pulsair Systems, Inc. of Bellevue, Wash. The Pulsair system sends pulses of compressed air through a hollow wand or probe. At the distal end of the wand is a flat circular shaped accumulator plate, such as a 4 to 6 inch metal accumulator plate. The accumulator plate helps to shape the released pulse of air to more effectively mix, and when mixing, is preferably positioned near the bottom of the tank. A Pulsair controller is located at the operator end of the wand. The Pulsair controller allows an operator to control the frequency of the pulses and the pressure of pulses. In use, the sudden release of air shocks the crosslinking liquid. As the air squeezes out between the plate and tank floor, it sweeps out the heavier liquids and solids. The air then accumulates above the plate into a very large, single oval shaped bubble. The bubble rises to the surface, a vacuum is created that pulls the heavier bottom liquids and solids up with it. As the bubble rises it also pushes the liquid above it up and out towards the tank perimeter. The liquid moves toward the sides of the tank and travels down the tank wall to the bottom.
To mix the crosslinking composition using the Pulsair system, the Pulsair wand and accumulator is inserted into an opening or bung in the tank. The operator selects a suitable frequency and air pressure, attaches a source of compressed air or gas (such as a compressor which may form part of the Pulsair system) and mixes for a period of time (for instance, a 360-gallon drum may require 20 minutes to two hours of mixing using 40 to 120 psi pressure at a frequency that can be varied, such as from 10-60 cycles per minute). The crosslinking product can be pumped to the asphalt/polymer product while mixing. When finished, the Pulsair mixer is removed from the drum or tote. While not arduous, the spillage or splash out from the open container and drippings from the mixer wand after removal can result in an unwanted discharge of product to the ground, which creates an unsafe and dirty operator environment. A better method of mixing is needed.